Field of the Invention
The present invention provides an electrodeless lamp, and particularly, to an electrodeless lamp capable of providing a continuous full spectrum radiation.
Descriptions of the Related Art
In conventional gas discharge lamp technologies, such as high-pressure mercury lamps, low-pressure mercury lamps, short-arc xenon lamps, long-arc xenon lamps, metal halide lamps, and high-intensity discharge (HID) lamps, light spectrums of different bands and proportions are provided by filling the lamp bodies with various gases or additives and using electrodes to excite the filling substances.
However, because the filling substances have different aging properties, the high temperature generated during long usage time and operation tends to initiate chemical reactions between the electrodes and the additives, and this may cause a change in the spectrum of the gas discharge lamps and intensity attenuation. Furthermore, for lamps adopting the aforesaid gas discharge lamp technologies, an external filter is often disposed to adjust the spectrum output, but disposition of the external filter degrades the light emission efficacy of the overall lamp source. In addition, the filter sheet tends to age due to long exposure to light radiation.
To overcome the aforesaid shortcoming, electrodeless lamps (also termed plasma lamps) have appeared. The electrodeless lamp, which is also a kind of gas discharge lamp, provides a light source by filling a sealed and transparent lamp body thereof with a chemically inert gas and one or more active components (e.g., mercury, sulfur, selenium, tellurium or metal halides) and exciting the filling substances by use of radio frequency (RF) or microwave energies.
The electrodeless lamp has a service life of up to about 40,000 to 90,000 hours which is much longer than that of currently known light emitters (including LEDs), and is capable of maintaining consistent spectrum properties even after a long time of use; moreover, the color rendering index (CRI>95) of the spectrum of the electrodeless lamp is the most similar to that of the sunlight among all currently existing light emitters.
Since the 1970s, the development of electrodeless microwave sulfur lamps has been initiated by experts such as Childs et al. The microwave sulfur lamp is a kind of full-spectrum electrodeless lamp driven by a microwave generator. A quartz bulb housing of the microwave sulfur lamp is filled with sulfur, and microwave radiation of 2,450 MHz is provided to excite the sulfur and heat the sulfur into the plasma state at an extremely high temperature, thereby, generating a continuous spectrum. The microwave sulfur lamp has the following advantages: high efficacy lighting, long service life, continuous spectrum, mercury-free, good luminous maintenance rate, and instant activation or the like. About 73% of the light emitted by the microwave sulfur lamp falls within the visible spectrum while the harmful ultraviolet rays only account for less than 1% of the light.
The related art of the electrodeless lamps has been disclosed in many patent documents, e.g., U.S. patents U.S. Pat. No. 5,404,076, U.S. Pat. No. 5,866,980A, U.S. Pat. No. 6,469,444B1, U.S. Pat. No. 5,606,220A, U.S. Pat. No. 5,866,981A, U.S. Pat. No. 6,633,111B1, and US 2010/0117533A1. However, most of the patent documents place an emphasis on adjusting the species and conditions of the filling substances so that the spectrum range, light emitting efficiency, and color rendering performance of the lamps are more suitable for application in general lighting.
In the industry, solar simulators are widely used in the performance evaluation of photovoltaic cells. The solar simulator provides, through the design of an optical system, a light source with properties consistent with those of natural sunlight received on the surface of the earth, thereby, ensuring accurate and reproducible test results.
In order to integrate and specify spectrum properties and the measurement of the solar simulator, standards such as IEC 60904-9, ASTM E927-10, JIS C 8912, CNS 13059-9 and test specifications for photoelectric elements such as IEC 61215 and IEC 61646 have been established internationally. According to these specifications, the measurement of a standard photovoltaic cell shall be performed with an incident light source with an intensity of 100 mW/cm2 and meeting the AM 1.5 G standard.
As shown in FIG. 1, in the related art, the light emission spectrum distribution of the current sulfur lamp used in general lighting is relatively narrow. The light emitted mainly falls within the visible light spectrum range, and the proportions of the light falling within the ultraviolet light spectrum and the infrared light spectrum are all relatively low, so it does not meet the aforesaid specification. Therefore, improvements with different combinations of (xenon) discharge lamps and halide lamps are often used as the standard light source of the solar simulator. Additionally, an appropriate filter may also be disposed to calibrate the emitted light spectrum.
As described in U.S. patents U.S. Pat. No. 5,866,980A and U.S. Pat. No. 6,469,444B1, although the spectrum performance of the sulfur lamp can be modified by adding a tiny amount of metal halides into the sulfur lamp, excessive metal halides tend to chemically react with sulfur, and this makes the sulfur lamp hard to activate or lit repeatedly. Therefore, there is a limit to the added amount of metal halides which increases the spectrum ranges of the ultraviolet and infrared light.
Accordingly, it is important to provide an electrodeless lamp which can generate a continuous full spectrum radiation and meet the AM 1.5 G standard to overcome the aforesaid drawback.